Power transmission systems adopting a magnetic-field coupling method are known as typical wireless power transmission systems. In such a power transmission system, power is transmitted from a primary coil in a power transmission apparatus to a secondary coil in a power reception apparatus using the magnetic field. Since electromotive force is greatly affected by the magnitude of a magnetic flux passing through each coil when the power is transmitted using the magnetic-field coupling in the power transmission system, the relative positional relationship between the primary coil and the secondary coil is required to have high accuracy. In addition, since the coils are used, it is difficult to reduce the size of the apparatuses.
In contrast, wireless power transmission systems adopting an electric-field coupling method are also known. The wireless power transmission systems adopting the electric-field coupling method are disclosed in, for example, Patent Document 1. In such a wireless power transmission system, power is transmitted from a coupling electrode in a power transmission apparatus to a coupling electrode in a power reception apparatus using the electric field. The accuracy required for the relative positions of the coupling electrodes is relatively low in this method and it is possible to reduce the size and the thickness of the coupling electrodes.
The power transmission apparatus described in Patent Document 1 includes a high-frequency high-voltage generation circuit, a passive electrode, and an active electrode. The power reception apparatus includes a high-frequency high-voltage load circuit, a passive electrode, and an active electrode. The active electrode of the power transmission apparatus is adjacent to the active electrode of the power reception apparatus with a gap interposed therebetween to achieve electric-field coupling between the two electrodes. The passive electrode of the power transmission apparatus, the active electrode of the power transmission apparatus, the active electrode of the power reception apparatus, and the passive electrode of the power reception apparatus are arranged so as to be parallel to each other.
Patent Document 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2009-531009.
In the wireless power transmission system adopting the electric-field coupling method described in Patent Document 1, high voltage (about 1,000 V) is applied between the active electrode of the power transmission apparatus and the active electrode of the power reception apparatus. Accordingly, it is necessary for the power reception apparatus side to reduce the high voltage to low voltage (about 10 V). General voltage reduction methods include, for example, voltage conversion using a transformer and voltage conversion using a direct current-direct current (DC-DC) converter. However, there are problems in that it is difficult to reduce the size of the transformer using winding and it is difficult to realize both a high voltage conversion ratio (the voltage reduction from high voltage of about 1,000 V to voltage of about 10 V) using the DC-DC converter in related art and high-efficiency drive.